linux-kernel - Re: [PATCH v5 1/4] smpboot: introduce SDTL_INIT() helper to tidy sched topology setup

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Message-ID: <xhsmhqzym1z4b.mognet@vschneid-thinkpadt14sgen2i.remote.csb>
Date: Fri, 11 Jul 2025 18:16:52 +0200
From: Valentin Schneider <vschneid@...hat.com>
To: K Prateek Nayak <kprateek.nayak@....com>, Li Chen <me@...ux.beauty>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>, "Rafael J . Wysocki"
 <rafael.j.wysocki@...el.com>, Peter Zijlstra <peterz@...radead.org>, Sohil
 Mehta <sohil.mehta@...el.com>, Brian Gerst <brgerst@...il.com>, Patryk
 Wlazlyn <patryk.wlazlyn@...ux.intel.com>, linux-kernel@...r.kernel.org,
 Madhavan Srinivasan <maddy@...ux.ibm.com>, Michael Ellerman
 <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>, Christophe
 Leroy <christophe.leroy@...roup.eu>, Heiko Carstens <hca@...ux.ibm.com>,
 Vasily Gorbik <gor@...ux.ibm.com>, Alexander Gordeev
 <agordeev@...ux.ibm.com>, Christian Borntraeger
 <borntraeger@...ux.ibm.com>, Sven Schnelle <svens@...ux.ibm.com>, Juri
 Lelli <juri.lelli@...hat.com>, Vincent Guittot
 <vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel
 Gorman <mgorman@...e.de>, Thomas Weißschuh
 <thomas.weissschuh@...utronix.de>, Li Chen <chenl311@...natelecom.cn>,
 Huacai Chen <chenhuacai@...nel.org>, Bibo Mao <maobibo@...ngson.cn>,
 Tobias Huschle <huschle@...ux.ibm.com>, Mete Durlu <meted@...ux.ibm.com>,
 Joel Granados <joel.granados@...nel.org>, Guo Weikang
 <guoweikang.kernel@...il.com>, Swapnil Sapkal <swapnil.sapkal@....com>,
 linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH v5 1/4] smpboot: introduce SDTL_INIT() helper to tidy
 sched topology setup

On 11/07/25 11:20, K Prateek Nayak wrote:
> Tangential discussion: I was looking at this and was wondering why we
> need a "tl->flags" when there is already sd_flags() function and we can
> simply add SD_OVERLAP to sd_numa_flags().
>
> I think "tl->flags" was needed when the idea of overlap domains was
> added in commit e3589f6c81e4 ("sched: Allow for overlapping sched_domain
> spans") when it depended on "FORCE_SD_OVERLAP" sched_feat() which
> allowed toggling this off but that was done away with in commit
> af85596c74de ("sched/topology: Remove FORCE_SD_OVERLAP") so perhaps we
> can get rid of it now?
>
> Relying on SD_NUMA should be enough currently. Peter, Valentin, what do
> you think of something like below?
>

I remember asking myself the same question when I mucked about the SD
flags; I ended up convincing myself to let it be but I couldn't find any
note as to why. Looking at things in their current state, I agree with you,
we could just bin it.